All day long, Leslie Schwab gripped a computer mouse at work, painstakingly clicking details onto computer drawings of historic Native American ruins for the National Park Service's historic American buildings survey.

Ten months after starting her job, Schwab could no longer hold the mouse, write with a pen or brush her teeth without a burning pain. She tried physical therapy, wrist braces and anti-inflammatory drugs but none provided relief. Distraught, she took her doctor's advice and left her job.

As one of thousands of workers suffering from a broad class of disorders known as repetitive stress injuries (RSI) or cumulative trauma disorders, Schwab's story had a relatively happy ending. After consulting with five doctors and undergoing a six-month program of physical and occupational therapy, the 26-year-old unemployed former Washington resident has regained the use of her left hand.

Complaints of repetitive stress injuries have grown by epidemic proportions in the workplace in recent years, despite the fact that many of them are difficult to diagnose. Still, there is a great deal of controversy about what they are and how prevalent they are. According to a recent hand surgery textbook, the condition "defies exact definition." The terms repetitive stress injury and cumulative trauma disorder have been applied to a broad class of symptoms including pain, numbness and loss of strength caused by repeated movements. These range from textbook diagnoses such as carpal tunnel syndrome, in which there is detectable nerve damage in the wrist, to complaints of problems in the hands, arms, neck and shoulder for which there are no clear, generally accepted physiological explanations.

Some skeptical physicians regard any complaints outside the textbook diagnoses as the mere aches and pains of unconditioned bodies, much like the stiffness an out-of-shape gardener feels after the first nice Sunday outside. But others say their patients' symptoms are so persistent that they must be suffering from a little-understood injury. One theory is that chronic, repetitive motion in one area -- especially if combined with high force, vibration or awkward postures -- produces an inability of the body's soft tissue, such as muscles, tendons or nerves, to recover.

Historically, these injuries have been most common in blue-collar industries such as meat packing. But between 1978 and 1991 the incidence of work-related repeated motion disorders among office workers grew about sevenfold. During this same period, the proportion of workers using computers also surged, from about one-quarter of the work force a decade ago to almost half of all workers today.

Once viewed as a disease primarily of middle-aged people, the disorder is also now assailing younger people, including workers in their mid-twenties whose entire working life has been spent on computers. At colleges across the country, students are starting to report repetitive stress injuries. Some experts blame crowded, badly designed workstations on campus, where students are forced to fulfill the requirement that term papers be computer-typed.

Cases of disorders associated with repeated trauma now account for 65 percent of all occupational illnesses, or about 332,000 cases in 1994, according to the Bureau of Labor Statistics. The single most common repetitive motion injury causing employees to miss work -- accounting for 43 percent of cases -- is carpal tunnel syndrome, a nerve disorder resulting from pressure on the median nerve at the wrist.

But specialists say other repetitive stress injuries are often overlooked because patients and doctors concentrate on the hand and the carpal tunnel. Some of these injuries include de Quervain's disease, a form of tendinitis in the thumb area; trigger finger, the locking of a finger in a fixed position; tenosynovitis, in which the tendon's sheath produces excessive fluid, causing the area to become swollen and painful; and muscle pain. Is It Real or Is It Hype?

What accounts for the remarkable rise in repetitive motion complaints? The question is the subject of heated controversy within the medical profession. Experts in occupational health and physical rehabilitation tend to regard the disorders as a product of increasing automation and revved-up productivity in the modern workplace.

Office workers' motions, like those of assembly-line workers, have become less varied, more static and more repetitive with the transition from manual typewriters to computers, observed Barbara Silverstein, director of safety and health assessment research at the Washington state Department of Labor and Industries. Silverstein's widely cited research, published in 1987, found that people in jobs with movements that were highly repetitive and required great force run an increased risk of suffering a repetitive stress injury.

"When you had manual typewriters, you had to walk to file cabinets, you had to stick paper in the typewriter, you had to turn the carriage. Before electric typewriters, you had to move that carriage return arm to start a new line," Silverstein said. "If you have an electronic library, E-mail and computer file systems, then you're stuck in one position."

Sitting up straight at a keyboard works the muscles harder than most people realize, according to ergonomics experts. Just to keep one's fingers prepared for typing without flopping on the keyboard requires contraction of the arm and shoulder muscles, impeding blood flow. At a typing speed of 60 words a minute, a computer user will hit the keys more than 100,000 times in a six-hour period.

Awkward posture is another risk factor. A typical head weighs between 10 and 12 pounds, about the same as a bowling ball. Poor posture will distribute this weight unevenly, forcing the shoulder and neck muscles to work harder, leading to chronic muscle strain.

"There's a failure on the part of the employee to regard himself or herself as an upper body athlete competing in a computer work Olympiad," said Emil Pascarelli, professor of clinical medicine at Columbia University College of Physicians and Surgeons, who runs a special unit for cumulative trauma patients at Columbia Presbyterian Hospital in New York City. Out-of-shape workers, Pascarelli said, are "not doing the necessary training to keep fit to overcome postural problems."

However, skeptics argue that the increase in reported injuries has been driven largely by media hype, heightened consumer awareness and the economic incentive of receiving worker's compensation payments for work-related illnesses.

"Most occupations have little or nothing to do with causing carpal tunnel syndrome," said Robert M. Szabo, chief of Hand and Microvascular Surgery at the University of California, Davis, School of Medicine. "People who have low-paying jobs, who work on assembly lines and have a lot of resentment against their supervisors, read in a trade union magazine that if they have problems they should go to a doctor. They say, Doc, I have carpal tunnel syndrome.' "

Szabo said only about 10 percent of his patients who come in complaining of repetitive stress have a diagnosable illness. Among patients who have a clear diagnosis of carpal tunnel syndrome, Szabo said, he frequently finds that they have one of the nonoccupational risk factors for the disorder. These risk factors include diabetes, obesity, a thyroid condition or a smoking habit. Carpal Tunnel Sometimes Misdiagnosed

The carpal tunnel is a bracelet of bone and ligament just below the wrist at the heel of the hand. Through it run nine finger tendons and the median nerve, which conducts impulses from the brain down the arm to the thumb, forefinger, middle finger and half the ring finger. Excessive up-and-down wrist and finger movements, such as those used in striking a keyboard, can irritate the tendons, causing swelling. The swelling puts pressure on the median nerve, causing the numbness and tingling associated with carpal tunnel syndrome.

Fluid retention caused by pregnancy can also increase pressure within the tunnel. Women account for the majority of carpal tunnel cases. One theory is that they are more vulnerable because they have smaller wrists than men but tendons that are the same size. Individual differences such as a person's ability to handle stress, physical conditioning and physical build also appear to play a role in the disorder.

The debate over causes is as much economic as medical. With repetitive motion complaints costing American industry at least $20 billion a year in worker's compensation costs, cost-conscious worker's compensation programs are putting pressure on doctors not to call the problems work-related and some managed health care groups are eager to downplay the condition, some physicians complain.

Even advocates for repetitive stress patients concede that the actual injuries and their underlying causes are not well understood. Part of the problem is that widely accepted diagnostic tests don't exist for many of the problems people are reporting. "We have very good ways of classifying and diagnosing carpal tunnel syndrome," Szabo commented, "whereas this amoeba of disorders called repetitive strain injuries never have any physical findings."

In the case of carpal tunnel syndrome, physicians can run a nerve conduction test to measure the velocity at which nerve impulses are transmitted. Electrical impulses slow down across damaged or compressed nerves. Although the test is commonly used, it is not foolproof. The line between normal and abnormal nerve conduction is not always clear, since some healthy people have naturally slow nerve impulses. According to one estimate, the test inaccurately identifies about 15 percent of patients as having carpal tunnel problems.

According to Pascarelli, "The problem is, generally speaking, rather superficial exams are done. There's a focus on the wrist, and carpal tunnel syndrome has been misapplied to the umbrella terminology, when it represents a small portion of what we see in these people who are injured."

In an unpublished study of 150 RSI patients, Pascarelli found only about 10 percent had carpal tunnel syndrome, while a majority had a harder-to-diagnose disorder known as thoracic outlet syndrome. This syndrome involves compression of nerves or blood vessels between the neck and shoulder. Symptoms include numbness in the arm or hand and a feeling that the arm is going to sleep.

One such patient is Rosalie Beck, 41, a self-employed landscape painter in Albany, N.Y. She was initially diagnosed with carpal tunnel syndrome -- she believes incorrectly. She consulted six doctors, one chiropractor and five physical therapists before she went to Pascarelli, who diagnosed thoracic outlet syndrome.

"Most of the physicians said, Oh, pain in the hands; it must be carpal tunnel,' " Beck recalled. "It's like focusing on the flea and missing the elephant." Although Beck is undergoing physical therapy, the problem is now so entrenched, she said, that she is unsure if she will ever be able to paint again. Frustrating Searches for Relief

Like Rosalie Beck and Leslie Schwab, many sufferers from repetitive stress injury report prolonged, frustrating searches for a cure. Few doctors treat the entire gamut of repetitive motion disorders. Many of these disorders are poorly understood, hard to diagnose and lack standard treatments backed up by research, advocates for repetitive stress patients said. Workers run the risk of losing their jobs when they take extended leaves from work in search of treatment. And even after undergoing treatment, including surgery, patients frequently complain that they have enduring pain or cannot perform such simple tasks as washing dishes, holding the phone or turning doorknobs.

Glenda L. Bob, 52, a typist at a preschool for handicapped children in Ithaca, N.Y., recently considered undergoing her third surgery for carpal tunnel syndrome because her hands were going numb again.

"I did feel a lot of relief afterward, but I would try anything before I had surgery again," she said, citing the inconvenience involved in recovering. Half of workers who undergo carpal tunnel surgery are out of work for four weeks.

If there's one lesson Leslie Schwab has learned, it's that preventing future injury will require constant vigilance. She now draws with a special writing apparatus that attaches to her hand, reducing the need for her to grip tightly. A "mouse nest," a horseshoe-shaped hand rest that surrounds the mouse, allows her to move the mouse without gripping. She does 10 stretches every morning for her arm and upper body and applies ice, heat and self-massage every evening.

Schwab was diagnosed with epicondylitis, also known as tennis elbow. The disorder is produced by the irritation of tendons on the back of the forearm, which are attached to muscles responsible for opening the hand. Some specialists report a high incidence of this problem in mouse users and musicians who grip their instruments too tightly. Schwab built up her drawing stamina gradually over several months, following her doctor's prescribed schedule. It started with five minutes of work interspersed with 10-minute breaks. "I need to take breaks, not be so tenacious," she said.

"If I go back to doing the same exact things," she added, "it will probably cause injury again." CAPTION: The most common repetitive stress injury is carpal tunnel syndrome. The carpal tunnel is a passageway just below the wrist at the heel of the hand. Through it run nine finger tendons and the median nerve, which conducts impulses from the brain down the arm to the thumb, forefinger, middle finger and half the ring finger. Excessive up-and-down wrist and finger movements, such as those used in striking a keyboard, can irritate the tendons, causing swelling. The swelling puts pressure on the median nerve, causing the numbness and tingling associated with carpal tunnel syndrome. Between 1978 and 1991 -- when the proportion of workers using computers soared -- the incidence of work-related repetitive stress injuries among office workers grew about sevenfold. Sitting up straight at a keyboard works the muscles harder than most people realize, according to ergonomics experts. Just to keep one's fingers prepared for typing without flopping on the keyboard requires contraction of the arm and shoulder muscles, impeding blood flow. At a typing speed of 60 words a minute, a computer user will hit the keys more than 100,000 times in a six-hour period. Experts advise that typists keep their wrists extended straight out from the hand, floating above the keyboard. They should not cock their wrists upward or flex them downward. Both positions increase pressure inside the carpal tunnel. CAPTION: How to Avoid Repetitive Motion Injury

Prevention is the best cure for repetitive motion disorders, most experts agree. Here are a few of their tips:

Don't flex your wrists. While typing, keep your wrist extended straight out from your hand, floating above the keyboard. Don't cock your wrist upward, in a "policeman-stop-signal-style", or flex it downward. Both positions increase pressure inside the carpal tunnel.

Beware of wrist rests. Some experts believe these encourage computer users to cock their wrists upward and to press their wrists down on the cushion. Both motions increase stress on the median nerve. Experts who still recommend wrist rests say they should be used merely as a guide to keep wrists poised above the keyboard. Don't rest your wrists on them while typing.

Keep your keyboard low. A low keyboard makes it easier to keep the wrist in a neutral position. It also opens up your elbow angle. Bent elbows pinch the blood supply for the nerve at the elbow. Recent studies by Cornell University ergonomics professor Alan Hedge found that a downward-sloping keyboard, which follows the natural descending angle of your thighs in a seated position, helps keep the wrists in a neutral position.

Vary your tasks. Intersperse your typing with visits to the Xerox machine, the FAX machine or phone calls. Always doing the same thing overuses one set of muscles.

Take frequent breaks. At least once every half-hour, take your concentration off the computer for a few minutes. Stand up, stretch your palms upward, look out the window, stretch your body.

Get into shape. Office workers who engage in regular exercise, like jogging or walking, and are not overweight are less likely to have problems.

Use good posture. People who develop repetitive motion problems often sit hunched over with neck forward, shoulders rounded. But sitting ramrod-straight for hours on end isn't advised either. Wriggle around in your chair every once in a while to relieve those muscles. Make sure your chair is the right height for you. Feet should be planted comfortably on the floor.

Use good finger technique. Women should keep nails short and fingers should be curved enough not to see the fingernails. Don't hyperextend your pinky or thumb. Don't use more force than necessary when hitting a key or moving the mouse.

Make your work station comfortable for you. Video screens should be placed straight ahead of you, not at an angle, which can cause a crimp in the neck. The middle of the screen should be a couple of inches below eye level. A screen placed too low forces you to curl your neck down.

What about the explosion of ergonomic equipment on the market, like new-fangled split keyboards, which can cost as much as $900? Despite the claims, there's been virtually no independent research on these products' ability to prevent problems. Some experts say they're like mattresses: Try them out for comfort but don't expect one type to fit all. CAPTION: Treating Carpal Tunnel Syndrome

The first line of treatment for carpal tunnel syndrome "is usually to try to understand what has caused the pressure on the nerve," said Peter C. Amadio, an orthopedic surgeon at Mayo Clinic in Rochester, Minn. Increasingly, for other repetitive motion complaints as well, that means looking at the patient's computer workstations or tools and modifying them to reduce awkward postures or excessive gripping.

Conventional treatment for carpal tunnel syndrome may involve the use of anti-inflammatory drugs, such as Advil, and splints on the hand at night to avoid curling the wrist. Many doctors now believe that using wrist splints at work is ill-advised, because it can cause the muscles to atrophy, squeeze the median nerve and force the patient to work in an awkward position that puts strain on other parts of the body.

Some doctors advise one or two cortisone injections to reduce inflammation and pain. Repeated injections of cortisone in the same area can cause tendons to break, however.

Vitamin B6 enjoyed a recent spate of popularity among repetitive stress patients as a self-administered cure, but doctors caution patients about it. If used in high doses like 1,000 milligrams, B6 can cause permanent nerve disease, Amadio said. At 100 mg per day, he said, "the scientific evidence is relatively weak that it works and if it does, it has a small impact."

Although surgery is one of the best-studied treatments for carpal tunnel syndrome, physicians generally view it as a last resort. In addition, new research suggests that patients may not be as happy with the surgery as their doctors are.

The standard surgery for carpal tunnel syndrome is known as the "release" procedure. The surgeon cuts a ligament, known as the transverse carpal ligament, which runs across the top of the carpal tunnel -- the bracelet of bones and ligaments just below the wrist. The aim is to create more room in the carpal tunnel and release pressure on the median nerve that runs to the hand.

"In most people it's not a permanent cure but a permanent significant improvement," according to Amadio. He estimated that 40 percent of patients who undergo surgery are "more or less cured." But he added, "The majority have residual problems," such as occasional pain, numbness or loss of grip strength.

Glenn Pransky, chief of clinical services for the occupational health program and associate professor of medicine at the University of Massachusetts Medical School in Worcester, said the "universally positive impression" of carpal tunnel surgery among surgeons doesn't carry through to workers who have undergone the procedure.

"They're telling me, I'm having restrictions at work, I still have pain, my job had to be changed.' And some couldn't get back to their jobs at all," Pransky said.

In some cases, Pransky said, the workers were mistakenly diagnosed with carpal tunnel syndrome because their doctors relied too heavily on the nerve conduction test, which measures the velocity at which nerve impulses are transmitted.

Susan MacKinnon, professor of surgery at Washington University School of Medicine in St. Louis, said this kind of misdiagnosis explains the puzzling phenomenon of people who undergo several carpal tunnel surgeries but still have problems.

"That's probably because the only diagnosis these doctors will consider for cumulative trauma disorders is carpal tunnel syndrome," she said. "They label the whole thing as that, and the only option they have is surgery. So they'll do the carpal tunnel release and that won't make it go away and they'll do it over and over again, sometimes until the patient gets worse from having too many operations in the same area."

MacKinnon said many of the patients referred to her for carpal tunnel surgery by other physicians don't have the syndrome or have a very mild version in combination with more complex cumulative trauma disorders. "They aren't coming in and saying, I've got a little numbness in my fingers.' They're saying, I have pain going from the tip of my finger to the top of my head. . . . I can't put my eye makeup on anymore, I can't work at my keyboard.' "

MacKinnon said she believes the pain they describe is caused by underusing weak lower and middle back muscles, which are crucial to sitting up straight, and overusing upper back muscles by hunching forward.

Some surgeons, convinced that surgery cannot solve the broad array of repetitive stress injuries, have been trying alternative treatments. MacKinnon prescribes specifically designed physical therapy exercises to strengthen her patients' lower back muscles and urges them to do aerobic exercise. In a study of 64 of her patients, presented to the American Society for Surgery of the Hand in 1994, 90 percent said this approach relieved their most troublesome symptoms.

"I now operate on a minority of my patients," said Leo M. Rozmaryn, a reconstructive hand surgeon in Rockville, whose practice is about 45 percent repetitive stress injury patients. Rozmaryn said he has been able to reduce the number of his patients who need carpal tunnel surgery by prescribing a series of hand exercises for the wrist and tendons.

Richard Norris, director of the Bethesda Center for Repetitive Motion Disorders, uses diagnostic techniques and treatments that he developed in treating thousands of musicians. The most common error in technique for both musicians and typists, according to Norris, is the use of excessive force or tension. He noted that the greatest musicians are also the most relaxed.

"The problem with typists is very few people look at the technique, because the page that gets printed out looks the same whether you type with horrible technique or great technique," said Norris. "But for the musicians, the technique really influences the sound."

One of Norris's methods for teaching computer users to type with the least amount of tension employs biofeedback. The patient's upper back or arm muscles are hooked up to a computer, permitting the patient to observe his level of muscle tension on a video screen while typing.

As for the hodgepodge of treatments Norris uses -- heating pads, massage, acupuncture, strengthening exercises and physical therapy -- he doesn't have studies proving their effectiveness although he can point to some satisfied patients.

"Basically, we treat this stuff empirically," he said. "It's not really very scientific at this point."

Dissatisfied with conventional medical treatments and leery of surgery, repetitive stress patients form an eager market for alternative therapies. An interactive computer bulletin board on the Internet, "Sorehand," is replete with stories of patients who have tried vitamin therapy, self-massage, Rolfing and movement techniques like the Alexander technique, originally designed to enhance the performance of actors, singers and musicians.

"At this point, I've tried so many things that it's hard to know which have worked or which to go back to," said Holly Idelson, 32, a reporter at Congressional Quarterly Weekly Report. She has tried physical therapy, acupuncture, electrical stimulation and massage. She tries to fight off pain and fatigue in her hand and arm by dictating her weekly news stories into a computer equipped with voice-activated software.

Idelson was diagnosed two years ago with cubital tunnel syndrome, a condition caused by a compressed or irritated nerve at the elbow, and more recently with carpal tunnel syndrome. In addition to numbness in her pinky and ring fingers, Idelson suffers from aches that at times intensify to sharp pains, extending from the base of her thumb through her wrist to her lower arm, shoulder and neck. Of her various efforts at treatment she said, "Nothing cracked the code. There wasn't ever a point when it was gone." CAPTION: Leslie Schwab, formerly of Washington, demonstrates one of the exercises she does to treat her repetitive stress injury. CAPTION: Bethesda physician Richard Norris helpps patient Susan Nikseresht find the right position at the keyboard. CAPTION: Artist Leslie Schwab left her National Park Service job after repetitive stress injury made it painful for her to move a computer mouse or hold a pen. Stretching and therapy have helped, but she still must take frequent rests while drawing.